Method for preparing half-tone printing-plates.



No. 843,833. PATBNTBD APR. 2, 1907.

f LKBRN.

METHOD POR PREPARING HALF TONE PRINTING PLATES.

- APPLCATION FILED FEB. a. 190e.

nu: Nonms PETERS cm, wAsHlNm'ou. n. c.

LAWRENCE KERN, OF DAYTON, KENTUCKY.

METHOD FOR PREPARING-HALF-TONE PRiNTlNG-PLATES.

Specification of Letters Patent.

Patented .April 2, 1907.

Application filed February 8, 1906. Serial No. 300,043.

To a/ZZ whom t may concern.-

Be it known that I, LAWRENCE KERN, a citizen of the United States, andresiding at Dayton, Campbell county, State of Kentucky, have invented acertain new and useful Method for Preparing Half-Tone Printing- Plates;and I do declare the following to be a clear, full, and exactdescription of the invention, attention being called to the accompanyingdrawings, with the reference characters marked thereon, which form alsoa part of this specification.

The desideratum in the various processes in half-tone printing is toattain the proper effects and contrasts in dark and lights, as well as aproper soft blending from one into the other. Absolute high lights-thatis, clear white imprinted spaces-are difficult to obtain under presentmethods and with the printing-plates now used, and expensive methodsusing so-called overlays and underlays are resorted to, which give,however, only limited results.

The obj ect of my invention is to produce a a printing-plate which givesabsolutely clear high lights and self-blending vignettes, as well asproperly-blended effects, without the use of overlays or other auxiliarymeans.

In the following speciiication, and particularly pointed out in theclaim at the end thereof, is found a full description of my invention,together with its manner of use and method of preparation, which latteris also illustrated in the accompanying drawings, a half-tone platebeing used for purpose of illustration, and in which- Figure l shows across-section of a printing-plate in the first stage of its preparation.Fig. 2 shows the same in a later stage of such preparation. Fig. 3 showsthe same at` a still later stage. Fig. 4 illustrates a printing-plateprepared according to my process.

Fig. 5 shows the die-plate I use in the preparation of my improvedprinting-plate. Fig. 6 shows in cross-section both the printingplate andthe die-plate shown in Fig. 5 on top of the printing-plate and for thepurpose of acting upon the latter. Fig. 7 shows a crosssection of thecompleted printing-plate. Fig.

8 showsa portion' of the preceding figure onl a larger scale. y

In order to make myself better understood, I will now briefly recite theusual present method of producing a half-tone printingplate. A negativeon a sensitized glass plate is first produced by the usual photographingprocess through a screen, the latter being used to obtain the dotsnecessary to produce an ink-transmitting printing-surface orprinting-face on the plate. With the aid of this negative a photographicprint is made on a sensitized metal plate intended to form the half-toneprinting-plate. This plate is shown in section in Fig. l, in which Aindicates the metallic plate, and B its light-'sensitive coating, allconsiderably enlarged. The process under which this photographic 'printis made causes certain parts of this coating to become fixed on theplate, subject to the ac-l tion of the light, and the non-exposed partsof the coating remaining soluble are washed away, leaving the plate asshown in Fig. 2, in which b indicates those parts of the coating whichremain after the soluble parts have been washed away, a indicating theintermediate parts where the printing-plate, is now exposed. A printingdepth is now obtained by means of chemical etching, whereby the plate issubjected to the action of a chemical in form of a suitable acidsolution and Whereby the exposed parts are eaten away, as shown at a inFig. 3. This causes parts b,

protected by the non-soluble coating, to rei main, such parts producingthe so-called "dots, which constitute the printing-face of this plate.Contrasts in light and shade exist in such a photo-engraved reproductionby reason of the color value of the original copy, which has beenproportionally transmitted through the screen on the negative; butbecause the natureof the half-tone plate makes it necessary to makeprinting possible to'hold a dot even in its lightest portion, where itonly prints an unsatisfactory gray tone, the present half-tone is faultyand unsatisfactory. This is by reason that the dots which constitute theprinting-face are all on a level and equally subjected to the action ofthe .press-roller and equally affected thereby IOO engravers tools,routing-machines, &c., does not entirely overcome this defect. My methodproposes to dispense with all such make-ready devices and relies solelyon the printing-plate itself to obtain these desired effects, theprinting-plate being prepared in a certain manner accordingly.

I refer now to Fig. 4, which illustrates a printing-plate produced bymeans of my process. C may indicate a certain illustration or cut to beprinted, and D a vignette surrounding the same. The dots shown are thesurfaces indicated at b in Fig. 3, while the intermediate surfaceportions are the cavities produced by the etching and shownat a in Fig.3. The varying size of the dots is due to the action of thephotographing process first described, subject to the screen, and as theaction is modiiied by the light and dark portions of the subjectphotographed. The larger-sized dots, holding and transmitting more ink,produce the shaded and darkei` portions of the picture and the smallerdots the lighter portions. Pronounced high light effects are, however,not obtainable by reason of the pressure of the press-cylinder, whichaffects equally all dots of the printing-face, as before stated,including also the smaller dots, where, however, limited pressure onlyor none at all would be preferable. To overcome this defect, I lowermore or less and in a certain manner to be presently described suchportions of the printing-face as indicated at c, where I desire toproduce high light effects, thus removing such portions beyond theaction of the ink-roller and the presscylinder, as well as graduatingsuch action for the purpose of obtaining soft blends at points wheredark and light portions merge into each other. Especially around theedges of a vignette such blends enable me to obtain. highly-desirableresults without the aid of tools or press make-readies. For the purposeof such lowering I prepare a metallic die-plate E, (see Fig. 5,) havingprojecting portions e, which in location correspond to such parts in theprinting-plate where I desire high lights, as 'at c, (see Fig. 4,) aswell as blended effects-as, for instance, around the edge d of thevignette. At the same time the thickness of the intended printing-platebelow these spots c where such effects are desired is reduced by theremoval of metal thereat, as shown at a2 in Fig. 6, the lower one of thetwo plates being the printing-plate A in course of preparation. metal isaccomplished by a routing-machine or by gouging-tools and is strictlylimited to the places mentioned, so that the general thickness of theplate and the straight plane of its back as far as it serves for supportremain unimpaired. Next the die-plate E is placed on top of this latterplate, everything eing so arranged that the raised parts e of thedie-plate, the high lights c and blended This removal of portions d onone side of the printing-plate, and the reduced parts a2 on its otherside register with each other. The printing-plate is now subjected topressure applied by any suitable means to the die-plate, a suitableprotecting medium-as, for instance, a piece of leather F-having firstbeen interposed to prevent injury to the dots which constitute theprinting-face of the plate. This pressure is transmitted to theprinting-plate by the raised parts c only of the die-plate, and contactbetween the two is limited to these parts, the action being terminatedat proper time, so that the body of the die-plate between these parts edoes never come in contact with the face of the printing-plate. Theresults of this action are illustrated in Fig. 7, which shows thecomplete printing-plate in section, the high lights c and blendedportions d of the face having been depressed, the metal yielding on agradual uninterrupted curve into the hollowed out portions a2, whichresulted' from the previous removal of metal. The extremely fine dotsbeing now within the depressed portion c of the printing-face and on theupwardly-curved surfaces surrounding the same, (see Fig. 8,) it is clearthat the pressure of the tympan or roller affects them to a degreevaried and graduated by these curves, thus producing highly effectivelight tones, while at the saine time the gradual transition from thedeepest parts of these depressed portions upon the curved surfacessurrounding them to the normal level of the printing-face produces thedesirable softly-blended eiiect between extreme contrasts. I haveomitted to show the dots in the plate illustrated in Figs. 6 and 7,which in reality are scarcely discernible with the naked eye, and aretherefore greatly enlarged in Figs. 2, 3, 4 and also in the enlargeddetail, Fig. S, which shows the Yfinal stage of the plate as it appearsin Fig. 7 and when made according to the method described. Any cavitieswhich may remain on the under side of the plate after its face has beendepressed in the manner stated may be filled with solder or othersuitable substance to reestablish thereat a surface even with the backof such plate. This process is equally applicable to any photo-engravedplate or any other printing-plate as may be worked with my method. Vhilecopper and zinc are the usual materials used for such plates, I do notlimit myself thereto, and any equivalent substances or alloys, as wellas electrotypes and stereotypes, may be used.

It is evident that a complete die-plate to produce simultaneously alldepressions is not absolutely necessary, and they might be produced inanother method and by hand-tools one after the other.

It may be mentioned that my method requires no change in the present wayof mounting the plates.

TOO

In conclusion, it will be noted that my method distinguishes sharplyagainst all other processes in which pressure is applied to the entireplate, whereby the delicately-engraved printing dots and lines arealways more or less bruised and injured, resulting in adefective'blotchy impression, more or less blurred. In my method I applypressure only at limited portions of the printing-face and at suchportions only which, being depressed below printing contact, do notserve thereafter as any parts of the ink-transferring printing-face. Noparts of this latter from which actual printing takes place come incontact with the pressure-exerting medium which depresses the otherparts, and they remain, therefore, free from all possible bruises andinjuries, which in transmission during printing would result indefective impressions. My process may, therefore, also be carried out ina more positive and direct way and under use of hard-metal implements orhard die-plates, all positively applied at certain limited spots, thusobtaining better and well-defined results, as against the uncertainty ofmethods working with soft and yielding pressures of tympans, overlaysand other surfaces consisting of or built up of soft material.Furthermore, the printing of blended portions is transmitted by curved fparts of the printing-face, whereby a proper evenlygraduated transitionfrom light to shade is obtained. This refers to and is applicable to allparts of the printing-plate, its edges for vignette inish, as well as tothe surfaces surrounded by them.

Having described my invention, I claim as new- The method of producing aprinting-plate, of the kind here in view, and which method consists ofrst decreasing the thickness of the plate from its under side and belowsuch parts only of its printing-face which are intended to produce highlights and blended effects adjacent thereto, and of afterward depressingthese parts below the level of the printing-face by applying positivepressure directly against such face, contact of the pressure-exertingmeans being limited to the deepest portions only of the surface to bedepressed, and which portions yare caused to produce absolute highlights by being depressed below printing contact, additional surfaceportions adjacent to these deepest portions being also .drawn in, thetransition from the normal face being on a gradual curve so that theprinting on these curved surfaces takes place with an evenly-gradu atedcontact, whereby the blended e'ects adjacent to the high lights areproduced.

In testimony whereof I hereunto set my hand in presence of twowitnesses.

. LAWRENCE KERN. Vitnesses:

ALBERT J. BOWMAN, EDWARD W. BLUM.

